Hydromechanical propeller control for turbo-prop systems



March l5, 1960 w. E. DIEFENDERFER 2,928,476

HYDROMECH-ANICAL `PROF'EILLER CONTROL'. FOR TURBO-PROP SYSTEMS Filed May 17, 1955 2 Sheets-Sheet l INVENTOR WILL/AM E. D/E'FENDERFER A r ron/vsr March 15, 1950 w. E. DIEFENDERFER 2,928,476

HYDROMECHANICAL FROPELLER CONTROL FOR TURBO-PROP SYSTEMS Filed May 17, 1955 2 Sheets-Sheet 2 /NVENTOR w/LL/AM E. 0/ FENDERFER 81%/ d ATTORNEY intr.. .l

HYDROMECHANICAL raoPnLLER CONTROL FOR TURBO-PROP SYSTEMS William E. Dieienderfer, Wethersfield, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application May 17, 1955, SeraiNo. 508,882

14 Claims. (Cl. 170'-160.2)

This invention relates to propellers and more particularly to controls for regulating the pitch of the propeller blades.

' It `is an object of this invention to provide a propeller control for propellers driven by turbine or other similar power plants.

It is a further object of this invention to provide a propeller control having a variable pitch stop or pitch limiting system. The pitch stop system may or may not supplement positive mechanical pitch stops.

It is a still further object of this invention to provide a means responsive to a power lever setting for reversing the governor sense, including mechanism for permitting a rapid switchover from positive blade angle control Vto negative blade angle control.

Another object of this invention is to provide a pitch stop and feedback system.

A further object of this invention is to provide a feathering and unfeathering system operated by a separate condition lever which provides for unfeathering to either an adjustable propeller speed or an adjustable blade angle.

Still another object of this invention is to provide a propeller control system which includes mechanism for featherin'g the propeller by several dilerent means.

These and other objects of this invention will become .readily apparent from the following detailed description of the drawings in which:

Fig. l is a schematic illustration of a turboprop power plant having a fuel control coordinated with a propeller control according to this invention.

Fig. 2 is a schematic illustration of the propeller control of this invention.

of the feathering solenoid 4section 16. ri`he power plant may be of any type such ythat one of the turbine stages drives a variable pitch jpropeller i8. The propeller may be of the type shown and described in the Forman Patent No. 2,477,868.

A fuel control 2G is provided for controlling the flow of .lluid from the supply tank 22 and thence via a line 24 `to the combustion section 14. The fuel control may be -of any desired type but the one illustrated herewith senses linlet air temperature via the line 26, speed via the connection 28 andcompressor discharge pressure via the line .30. A control `sensing these parameters vis, fully disclosed in patent application Serial Number 244,551 by Stanley G; Best, ined August 31, '1951. 'me fuel control 2o 'is controlled by apower lever 34. The power lever 34 is also connected to the propeller control 36. 'Ihe propeller controlf3`6 is set by the power lever 34 and also-by a condition lever 38. The functions of the power lever 2,928,476 Patented Mar. 15,y S1960" 34 and the condition lever 38k are described in more dtail i y hereinafter in connection with Fig. 2. l

T he propeller control 36 is more clearly illustratedin the schematic systemV shown in Fig. 2.-. inasmuch as the control has a number of operative functions, only por-V tions of the system will be described at atirne for reaof clarity. However, a brief overall identification of the major elements will be presented. VFirst of all, the

power lever 34 of Fig. 1 rotates the pulley 40 while the condition lever 38 of Fig. l rotates the pulley 42. The' pulley 40 operated by the power lever 34 vinturn rotates the gear segments 44 and 46, shaft 48 and nally the gear segment of the shaft 52. TheV shaft 52 is intended'tn control a speed setting cam 54 and'anticipator cam 56,V a reverse governing switchover cam 58,V a high pitch stop cam and a low pitch stop'cam 62.v The pulley 42",*ori

the other hand, responds to movement of the condition lever 38 and rotates a second shaft l64 which inturn rotates a speed depressing cam 66and unfeatheringy 68 and a feathering cam 70. The function of each of the cams will bedescribed in connection with the particular mechanism which they are intended 4to actuate.

First of a1l,'the speed setting system comprises primarilyv the speed setting cam 54 which moves the cam" follower 74 carried by a bell crank' 76 which is pivoted at 78 and hask one arm 80 carrying a roller V8,2Nv`vhich engages a rod 84 connected at 86 to another rod 88'Which carries a moveable roller at Vits extreme right end. Motion of the speed setting cam 54 will transmit motion to the rod 84 to the connection 86 which, in turn, will move the speed setting pilot valve 92 so as to control the ilow of iiuid to the chamber 94 of the speed setting servo 96. The speed setting servol 96 includes a piston 98 which engagesv a link rod 100. The rod 100 at itsrighthand end is connected to the roller 90,v hence4 the speed,` setting servo piston 98 positions the -roller 90 so as to" change the 'compression on the speederspring 102 ofthe pilot valve 184. The pilot valve 104 then in turn con-` trols the ilow of high pressure fluid to the main control servo cylinder 106 ,shown at the top'of the drawing.

It will be noted that theservo cylinder 106 comprises a stationary piston 108 which has Aits left-hand area 110 larger than the iight-hand rea 112. The right side 112 of the piston `is continuallyexposed to high pressure llluid from a pump 114 adjacent thereto via'a line 11,6. The n left-hand side of the piston llS'is supplied with either high pressure or drain pressure via "the line 1 18. With high pressure supplied' tofthe side 110, the overbalancing force will tend to move the cylinder 106 to the left and when low pressure fluid is supplied to the side 1-10 the cylinder 186 will move toward the right. The motion of the cylinder 106 is transmitted to a rack 120 Vand a pinion 122 which, in turn, may be operatively connected tothe propeller control or distributor valve such as thatY shown in Patent Number 2,664,960 issued to Longfellow et al. Y

For reasons of clarity, itis best to describe a complete cycle of increasing r.p.m. and a cycleV of decreasing r.p.m. to define the function of each of the elements in the primary speed setting system. In order to increase the r.p.rn. setting, the power lever rotates the speed s'etting cam 54 in `a clockwise direction. As the cani 54 rotates clockwise the cam follower 74 moves to the right, therebyV raising the arm 80 and the roller 82 and .perf

mitting the rod 84 vandr its connecting point 86 to movev upward. This upward motion results from the factthat the speed setting pilot valve 92 hasV its bottom land 'conf'l tinuously exposed to high pressure uid of the line 130.

The path of this high pressure uid will be described .here-V inafter in connection withmthe movement of the governor pilot valve 104. As'the speed setting pilot valve 92 i's moved upwardly the high pressure uid'fro'm theline 130 passes to the line 132, through a rotating chopper valve 134. The chopper valve permits ow only during a portion of each revolution so as to increase .the

time. constant of therspeed Asetting `servo system. High pressure iluid ows throughthe chopper valve to the line 136 `and then to the chamber 94 of the speed `setting'servo 96. `This causes the piston 98 to move upwardly and the rod 100 `to pivot clockwise about its pivot'point 138 so that the roller 90 on top of the governor-control valve .104 islmoved downwardly. The downward movement of the roller 90 compresses the spring 102 and this force is transmitted through the sleeve 140 and through the springu142 tothe -valve stem 104. Downward movementof the valve stem 104 connectsthe high pressure line 146 with the line148 leading from the governor ontrolrvalve. In this position of the pilot valve the flowl side of the servo piston 108. This moves the cylinderV 106 to the left toward a low pitch or increase r.p.m.

position. Y Y

' It should be notedthat as the speed setting pilot valve 92 was moved upwardly so as to move the speed setting servo piston 98 upwardly, the rod 100 rotated clockwise so as to move the roller 90 at the right-hand end downwardly. This downward'motion of the roller 90 is also transmitted to the rod 88 such that the point 86 is moved downwardly a proportional amount. The downward motion of the point 86 tends to neutralizerthe speed setting pilot valve 92 so as to prevent any further change in setting of the main pilot valve Speeder spring 102.

` As the main control servo cylinder 106 is movingto increase r.p.m. it carries withV it a depending arm 162 which has integral therewith three reciprocating cams 164, 166'and4168l The .operation of only cam 164 will be described at this point. In" the position shown, the cam 164 as ,it moves to the' left will cause the follower 170 to move clockwise about its-pivot 172 so as to raise the roller 174 which engages Ythe rod 176. Since the rod 176 isconnected at 138 to the rod 100, the rod 100 is permitted'to move upwardly about its left-'hand end so as the compression on Speeder spring 102, providing a stabilizing effect on the control. .The foregoing describes a feedback` system for the governor control valve.

In order to decrease r.p.m., the speed settingcam 54 is rotated counterclockwise thereby moving the cam follower 74 to the left and rotating the valve crank 76 clock-V wlseto force roller 82 downwardly along with the rod 84 and the-pointv 86. Downward motion ofthe point 86 moves the stem of the speed setting pilot valve downwardly so that the line 132 is connected .to` drain. This drain pressure is then conducted through the chopper valve 134, line 136 to the chamber 94 of the speed setting servo 96. This moves the speed settingservo piston 98 downwardly thereby permitting the rod 100 to rotate Motion of the. Yservo cylinder Vtoward low pitch thus temporarily'relieves permitsthe tlyweights to raise the control valve to connect the line 148 to drain pressure passing through the ,central aperture 180. and the passage 182. Drain pressure in the line 148 passes to the line 158 and thence to the line-118 leading to the left-handY side 110 of the main control servoA piston 108. This in turn causesA the servo cylinder. 106 to move tothe righttoward a high pitch or decrease r.p.m. position. The feedback to the control valve through the cam 164 is the same as described above except that it operates in a reverse direction. y

The throttle derivative or anticipator. feature of this control is required onV propeller engine combinations in which the power arid speed schedules are coordinated and both controlledby one pilot' operated lever. In such installations, an increase in speed setting is usually accompanied by an increase in engine power, which usually results in the bladeangle having to either stay approximately constant orincrease.A Normally, if the Vspeed setting of a propeller is increased the blade angle has to decrease to unload the engine andl increase the speed. lt is thus apparent that for most'coordinated installations the control must either cancel or override the decrease pitch signal vresulting from an increase in the speed setting. The anticipator cam 56 attachedto the power lever sends a signal directly to the Speeder spring with very little time delay. The anticipator cam motion being applied to the speeder springis bled off through the time delay system. Thus, ify cam '56 rotates clockwise, speed setting cam 54 is increasing speed 'setting through its crank arm 76 and rod 84, so that the lei't-emndv of rod 176 moves down, about point 138, releasing compression on the Speeder spring. This will increase the blade angle. As the point 90 on top of the Speeder spring moves upward, the speed setting pilot valve -92 is raised by way of rod 88 causing the speed setting servo to raise.

Raising the speed setting servo 92 causes the speed setting servo element 98 to move upwardly. so that rod 100 rotates clockwise about point ',138 and hence wipes out the anticipation signal whichhadv been sent to point 90 on top of the Speeder spring'Y 102.

It should be pointed out that although individual actions such asspeed change, feed back and anticipation have been separately described, these actions operate more Y or less in cooperative unison sothat stable operation is prop system the propeller and its control establish r.p.m.`

control of the propeller and turbine during night conditions. However in Beta control (ground handling and reversing) the propeller control `schedules a blade angle and the engine fuel control controls r.p.m.

p During night conditions any change in load on the engine where there is no movement of the power or con- Y dition lever is corrected by the blades changing pitch.

` speeds-require increase pitch operation.

kcontrol governor performs this on-speed function. Speed settings during night are controlled by the power lever.

Underspeeds are corrected by decreasing pitch and over- The .propeller The power lever` establishes `a fuel flow setting for the fuel control and sends a signal to the' propellercontrol. The iirst signal felt by the prop control is an anticipation signal which begins moving the` blades toward the desired position corresponding to the` new fuel flow setting. This anticipationgsignal is erased by the feed-back systerrr Y, The propeller receives 4through the time delay system a second speed setting `signal to accomplish` what the `pilot is, calling for 'withthe new power lever setting. This second signal isin accord with the fuel ilow setting and the `prop and engine lsettle outonY this new power setting. i

During ground handling the` propeller control i is scheduling a blade angle and the fuel control is scheduling r.p.m. and fuel flow, The power lever is setting both thecontrol. The propeller control does act as a topping governor dusting reversing but the fuel control setting is lower than the prop setting and the prop governor is acting ttherefore as a safety feature.

Although thepropeller such as disclosed, for example, in the abovelreferred-to Forman patent mayinclude mechanical stops such as feathering and reverse stops and also disengageablelow pitch stops for a positive range of operation, this control provides further pitch stops within the control itself. These stops are intended to prevent an undesirable output signal from the main control-servo cylinder 106. The pitch stop system is intended Vto provide a stop which is variable through both the positive pitch r'a'nge andthe negative pitch range. Hen4ce,'the stop system is intended to prevent the propeller blades frombeing moved to some lower pitch than the set pitchin the positive range. In the negative range, the blades are prevented from going to some higher pitch 'than theV desired pitch or, in other words, the blades are prevented from moving toward a less negative pitch.

The pitch stop settings are determined by the high pitch stop cam` 60 and the low pitch stop camV 62' which arerotated or positioned by the power lever. The cam 60 is adapted to be engaged by a cam follower 1'90 while f the cam r62 is adapted to be engagedby the cam follower 192. The cam follower 190 is attached to the leftendH of the beam 194 while the cam follower 192 is Vattached to the left end of the beam 196. The beams 194 and 196 are intended to pivot about 'cam followers 198 and 200 respectively. The cam followers 198 and 200 are fixed to piston rods 202 and 204' respectively. Thepiston rods 202 and 204 are actuated by pistons 206 and 208 whereby one or the other of the cam followers 198 and 200 are engageable with a 'cooperating cam. Thus, as shown, the cam follower 200 is in engagement with the cam 166 while the cam follower 198 is disengaged from its cooperating cam 168. The manner in which the cam 'followers 198 and 200 are engaged with or disengaged from their respective cooperating cams will be more clearly described in connection with the sense reversing system ofthis control. The beams 194 and 196 are attached at' theirl right-hand ends to rods 214 and 216 respectively. These'rods are, in turn, adjustably fixed toa rocker arm 218 which is pivoted at 220 and has its left end 222 in engagement with the bottom of the governor pilot valve stem 104. In the position shown, the low pitch stop cam 62 `is operative and hence for any position of the power lever the pitch stop cam 62 will position thev cam follower 192, the beam 196, beam 218 and hence' will position point 222 relative to the control valve stem104. Should' then, for example, the maincontrol servo cylinder 106 v begin tor move to call for a pitch which is lower than that set by the pitch stop cam 62, the motion of the servo cylinder 106 will be imparted at the same time to the cam 166. Whenthe cam 166 moves toward the left, for example toward a lower pitch position, the cam follower 200 will be lowered whereby the beam 196 moves clockwise about its left end 192. Hence the rod 21'6 will move downwardly rotating rocker '218' clockwise about its pivot 220 so that the end 222 physically moves the pilot. valve stem 104 upwardly from its neutral posi-v tion thereby calling for an increase in pitch.

In addition, when a new pitch position is set by the power lever, as for example, av` lower pitchthek governor control valve will be permitted to move downwardly to call for this' lower pitch and` as the main control servo cylinder moves the pitch stop system. will be adjusted duringthe change such thatwhen the proper'blade positionis reached the governor control valve stem'1`04 willA resting against'the end 2220i VtheV rocker 218. During the'v reverse range of operation, the beam 194 has its cam follower'198 moved intoengagement with vthe cooperating cam 168' while the cani follower 200 is disengaged from the cam -166 so that 4the high'pit'ch stop ca'rnv 60 will then `be setting the cam follower 1590 and the highc pitch limit system will be in operation. Again,l

it should be pointed out that the highpitch stop system prevents movement of the blades toward a less negative angle or toward the positive pitch ran-ge. Fixed mechanicalpitch stops' are also provided to limit the positive and negative pitch extremes of blade angle travel. Motion of the main cylinder 106 to the right, or to high pitch, is limited by the adjustable stop 276. Motion to the left, or to low pitch, is limited by the adjustable stop 274.

Fig. 2` also shows the reverse governing switchover system to provide for proper governor control in a'reversing sense and also provide a variable pitch stop vin Vthe reverse vrange'.

high pressure u'id via a line 240 which branches Voff the main high pressure linel 154 at the bottom ofthe drawing. High pressure fluid to the valve vilows to the line 242 Vbut due to the valve position this high pressure iluid does not pass through `the valve. However, high pressure iluid in the line ,240 continues upwardly and acts on the bottom of the switchover piston 206 and the top of the switchover piston r208, thus causing the piston 206 to be in a raised position while the piston 208 is held in a down-position. The down-position of the piston 208 provides engagement of the cam follower 200 with its cooperating cam 166 providing pitch stop variation in the positive blade angle range as described above. As shown in the drawing, the top side of thepiston 206 andr the bottom side of the `piston 208 are connected via line 246 to port 248 of the reversing valve 156 and in the valve position shown is connected to drain. In the event that reversing valve 156 is moved upwardly, the port 248 is no longer exposed to drain but instead isconnected with the line 242 so thatV high pressure ll'uid passes through the port 248, the line 246 and thence to the top of piston 206 andthe bottom of piston 208. Now, although both sides of these pistons are exposed tothe same pressure, the top of piston 206 and the bottom of piston 208 have larger area than their respective opposing sides `such that piston 206 will move downwardly and piston 208 will move upwardly. This causes pitch stop cam follower 198 to engage with its cooperating cam 168 'and disengages cam follower 200 from its cooperating cam 166. Thus, is provided a quickly operable means for putting the reversing range pitch stop system (high pitch stop cam operating) into operation.

As stated above, the reversing valve, in addition, has the function of reversing the sense of the governor and governor control valve. In the position shown in Fig. 2, the reversing valve connects the line 148 leading from the governor control valve to the line v158 which conducts Ahigh pressure fluid to the main control servo cylinder.

rhus, as the governor control valve stem 104 moves downwardly, high pressure iluid is connected to the line 148, while, if the valve stem rnoves upwardly drain pressure is connected to the line 148 through the port 182 and the passage 180. However, for controlling in the reverse range another line 254 is provided just above the line 148 leading from the governor'coutrol fvalve. When the reversing valve is moved upwardly the line 148 is blocked and the line 254 will then be connected to 4 the line 15S leading to the main control servo. Under these conditions,V then, kthe governorrwill act oppositely to the .manner in rwhich-it had inthe positive pitch range so that itghas a reverse sense.

'fhus,shold`the governor control valve stem 1043m0ve 3 upwardly thepressure line 146 will b e'connected to the line 254 so that high pressure fluid flows to the main Y To this end the reversing-valve 156 is provided. In the position shown, the valve 156 receivesV `In order to provide the above described switchover in a rapid fashion, a snap actiondevice is provided for actuating the reverse valve 156. To'this end, the valve` has connected thereto a'vertical. rod 262 which in turn is connected to one end of a rod 264 pivoted at266 intermediate the ends thereof. The other end of the rod 264 is operatively connected at 268 to the reverse governing switchover cam 58.V This cam is driven from the shaft 52 througha tongue 270 which is centered by aY pair of springs in` a slot in the cam 58. TA spring loaded detent 272 is also vprovided so that when the main power control lever is moved-from thefpositive to the` reverse range of propeller operation` thetongue 270 will compress one of the springs until there is a solid drive between the tongue andthe cam.v At this time, the earn will be moved past thedetent and there will be a positive and sudden movement of the cam as it is freed from the detent. This, in turn, will move the cam .follower 268 downwardly at a sudden rate so as torotate rod A264 and rapidly lift the rod 262 and shift the reversing valve. Hence, there is provided a no-dwell system for quickly switching over from Vpositive pitch range operation to a negative pitch range operation for governor sense and pitch stopoperation.A A

During feathe'ring and unfeathering a number of control elements come into play, however, the'k actual feathering system Ywill be described first. Y As seen in the upper left hand corner in Fig. 2, feathering valve cam 70 is rotated by the condition lever 38 of Fig. 1. The feathering valve cam 70 moves a rod 300 which in turn'rotates a bell crank 302 which operates a vertical rod 304. The rod 304 moves the central portion 306 of the feathering valve 152. Motion of the rod 300 to the right raises ythe rod 304'in the valve element 306 such that the line `158 leading to the line 118 and to the left side of the main control servo piston 108 can be connected to drain. Thus, as the feathering valve element 306moves-upwardly, the line 158 is then connected to the line 308 which then communicates with the passage 310 in the valve element 306 whereby fluid can pass upwardly to drain via the passage 312 in the casing of the feathering valve 152. By connecting the lines 158 and 118 toV drain via the line 308 the side 4110 of the main servo control piston 108 is exposed to low pressure such that f the cylinder 106 is moved to the right to'signal the propeller to increase pitch to the feathering position.

The propeller-may also be feathered by a feathering solenoid 320 shown schematically in the central right-hand side of Fig. 2 and also illustrated in detail in Fig. 3. The feathering solenoid 320 is connected to high pressure line 150 by means of a line 322 and is capable of 'convnecting this line to the line 324 leading to the feathering valve 152.v As seen in Fig. 3, when the switch 326 isclosed the .coil 328 of the solenoid valve 320 is energizedso as to move the plunger 330 to the left to unseat the spring loaded ball check valve 324. This permits communication from the line 322 to the line 324. As seen in Fig. 2, the line 324 leads to an annular chamber -332 inthe feathering valve. YWhen high pressure fluid is connected to the chamber 332 the force moves the central valve element 306 upwardly against the force of the upper spring and thereby connects high pressure lines 158 and 308 to drain via the passages 310V and 312.`

It will be noted that the Ifeatheri'ng` valve 152 also includes a lower moveable portion 340 which isin operative engagement with, but moveable with respect to, the central valve element 306 by means of a'spring 342.

Thus, the element 340 will normally move with the valve .7o athe value called for bythe speeddepressing cam66 and element 306 and the .element 340. may be physicallyv moved upwardly'to `forceably move the central valve element 306 in an upward .hfeathering position, the spring .342.being capable of transmitting suicient force to move element306 Yupward againstthe force of the upper spring. The lower valve element340 cany be actuated as, for example, by the member 346 connected to mechanism externally` of the control. The member346is actuated by an engine torquesensing device such that should there be a loss of power in the power plant the control would automatically signal to feather the propeller. In order to obtain a motion iof the element 346 inV response to a change in power plant torque, a mechanism such` as disclosed in Patent No. 2,444,363, Newcomb, may be used.

The feathering valve 152 is Anot actuated by the feathering valve cam 70 until the condition lever 38 of Fig. l has almost reached its feathering position.- As the condition lever is moved toward a feathering position the unfeathering carn 68 is also rotated along withV the feathering valve cam. The unfeathering cam 68 as it is moved toward the feather position engages the cam follower 69 so that the beam 196 connected thereto is raised to the extent ,that the cam follower 192 is lifted off thelow pitch stop cam 62. The beam 196, as pointed out previously, is connected to the vertical rod 216 and, in

turn, to the rocker 218 such that the main governor pilotV valve is forced-upwardly thus giving an artificial overspeed condition' and thereby sending to the propeller an increasebladeangle signal. Thus, the unfeathering cam is controlling blade angle up to the actual feathering position, and back down'to the normal governing range whenvunfeatherin'g, by varying the low pitch stop position for` the main governing valve. This provides a con` trol which in certain installations can bring the propeller pitch back to a given blade angle when the condition lever is moved back from the feather position to some intermediateunfeather positionfor air starting the particular power plant. i

In some propeller power plant installations it may be desirable to unfeather the propeller such that it is rotated at a given r.p.m. ratherV than unfeathering to a particular blade angle. To this end,the condition lever also operates a speed depressing cam `66. The speed depressing cam engages the bell crank 76 of the normal speed setting system as the condition lever is moved towardfeather position.V When the condition lever is rotated to the feather position, the speed depressing cam 66 rotates clockwise, this moves bell crank 76 clockwise about its pivot 78 whereby the normal speed setting cam 54 is disengaged. This motion sends an extreme decrease r.p.m. signal to the Speeder spring of the main control governor pilot valve. This signal, it will be noted, is in the same directionas the signal being produced at'the same time creasing low pitch stop setting. Both of these signals tend V specified speed.

to'raise the pilot valve to produce the extreme high pitch setting of the propeller blades. changing until the `condition `lever position is' reached when the feathering valveV 152 Vtakes over the actual feathering. f

v,When the pilot prepares to try an air start of the power plant the condition lever is moved such that the speed depressing cam 66 is rotated counterclockwise thereby positioning the main governor Speeder spring to call for a Y It should be noted that, in this range, the normal speed setting cam 54 is not yet functioning. The rst few degrees of movement ofthe condition lever returns the feathering valve 152 to its normal position so that nowpthe speed depressing cam is signalling the desired spring'settingto the speeder spring 102 of the main governorfpilotvalve. The propeller then will begin to unfeather and the windmilling speed will increase to These signals continue gi the contr lwill maintain "this desired 'r.p.'m`; After the' power plant has been started the condition lever will `be` moved toits runjposition such thatA the normal'speed '.setting cam 54 will take over control. It lisfthus possible. for the pilot to control the rateof'unfeathering, "the enginel windmilling or airl start r'.p;m. and the rate of engine acceleration from theY air' start rgpm. to thev normal governing range. The speed depressing cam calls for an r.p.m. which is lower than thelowest speed setting of the speed set cam 54. This insures a relatively highV pitch to provide a high driving torque'by the airstrearn and avoidsV too high an r.p.m. until a start is obtainedi A further feature ofv this invention is to provide a means for automatically adjusting Vthe Ymain governor pilot valve setting for synchronizing two or more power plants. This synchronizing may take the form of actual speed synchronization or it may be in the form of a phase synchronization. To this` end a. synchronizing valve 38d is schematically shown on the right hand .side of Fig. 2 and in more detail in Fig. 4. The synchronizing valve 33t) receives a supply of high pressurefluid via a line 382 and controllably varies this pressure and sends this varied pressure signal via the line 384 to a chamber 386. The upward force resulting from this pressure acts in pposition to the force of the speeder spring and is thus capable of biasing the speed setting of the governor. Since the pressure in chamber 386 is controllable by the synchronizing valve 380, the speedsetting ofthe governor can be varied over the range required for synchronizing two or more engines by the synchronizing valve. The synchronizing valve 3250, seen in Fig. 4, comprises a proportional solenoid 390 of the type shown, for example, in Patent No. 2,579,723, issued December, 25, 1951, to Stanley G. Best. The solenoid is intended to position a spring-biased apper element392which varies the opening of an orice 394. By varying the opening of the orice 394, the high pressure from line 382 is adjustably varied so that the pressure of the line 384 is controlled.

The signal being sent to the proportionalvr solenoid coils 390 may be obtained, for example, from a device as that shown in Patent No. 2,418,659, issued to W. S. Hoover. The signal may also be obtained from a device such as is illustrated and described in copending patent application Serial Number 508,868 filed by Stanley G. Best as of even date.

Although only one embodiment of this invention has been illustrated and described herein, it will be apparent that various changes and modications may be made in the arrangement and construction of the various parts without departing from the scope of this novel concept.

What is desired by Letters Patent is:

v 1. In a propeller having variable pitch blades, means for varying the pitch of said blades in positive and negative ranges, means for controlling said pitch varying means including a speed setting device, means for setting said speed setting device for control in both pitch ranges of said blades including operative connections to said device, and a second speed setting means for overriding said rst mentioned speed setting means to control propeller speed in the positive pitch portion of said pitch ranges including a manually controlled speed depressing mechanism for taking over control from said first-mentioned speed setting.

2. In a propeller having variable pitch blades, means for varying the pitch of said blades including a servo motor, means for controlling said pitch varying means including a control valve operatively connected to said servo motor, means for moving said control valve including a governor and speed setting means, means for temporarily resetting said speed setting means, a feedback connection between said servo motor and said control valve for wiping out said temporary reset, and means for permanently resetting said speed setting means including operative connections to said feedback connection.

'3; 'In a control for'apropeller'liavirig rrtovabl'e.pittili' blades, meanstfor varying the pitch `of said bladesjc'om' prising a servo. device, means Lfor controlling" said; pitch varying means :including a controlvalve operatively con nected to said' servo device, speed governor means for etfecting movement of said control valve, means fori' setting the speed .of saidV governor means', a pitch stop' mechanism operatively connected to said' control valve` for urgingvsaid'valve in opposition to-saidgovernor means in one direction, a fluid chamber operatively connected to said control valve,`and meansfor varying the pressure in said lchamber whereby said control valve is urged in one nected to said servo device, speed governor meanslfor" eiiecting movementY of said. control valve, means for setting the speed of said governor means, a pitch stop mechanism operatively connected .to said control valve for urging said4 valve `in opposition to said governor means and in onlyone direction, and a pair of cams movable in response to movement of said servo device, oneof said cams being operative to control said pitch stop mechanism in the positive pitch range of'said blades and the other of said cams being operative to control said mechanism in the negative pitch range of said blades.

5. In a pitch control for aV propeller having variable pitch blades, means for varying the pitch of said blades, means for controlling said pitch varying means including a speed governingV device and a control valve controlled by said governing device,.means providing blade pitch stop mechanism for preventing pitch change by positively actuating said' control valve in opposition to the inuence of said governing device and in; one direction, means .for varying said pitch stop mechanism over a range of blade4 pitch positions, means for reversing the sense of said controlling means in positive and negative pitchk positions of said blades, and Vmeans for simultaneouslyk reversingthe sense of said pitch stop mechanism.v l

6. In a pitch control for a propeller'having vvariable pitch blades, means for varying the'pitch of said blades, means for controlling said pitch varying means including a speed governing device, means providing blade pitch stop mechanism for preventing pitch change'in opposition to the inuence of said governing device on said control, means for varying said pitch stop mechanism, means for reversing the sense of said controlling means in positive and negative pitch positions of said blades, and means for simultaneously reversing the sense of said pitch stop mechanism.

7. In a propeller having variable pitch blades, means for varying the pitch of said blades including a servo device, a governor, a control valve operatively connected to said governor for controlling said servo device, means for reversing the sense of operation of said governor in the positive and negative pitch ranges of said blades, pitch stop means for limiting blade pitch movement includingV a cam operable in each of the positive and negative pitch ranges of said blades, means for selectively engaging one of said cams and disengaging the other of said cams, and means for operating said reversing means and said means for selectively engaging said cams.

8. In a propeller having variable pitch blades, means for Varying the pitch of said blades including a servo device, a governor, a control valve operatively connected to said governor for controlling said servo device, means for reversing the sense of operation of said governor in the positive and negative pitch ranges of said blades, pitch stop means for limiting blade pitch movement including a cam operable in each of the positive and negative pitch ranges of saidblades, means for selectively engaging one of said cams and disengaging the other of said cams, and a single valve operatively connected to said reversingl operating the same; -t L, Y Y

y 9L In a propeller having variablepitch blades, means means and said cam engaging meansrfor simultaneously while disconnecting the other of said sets, a pitch stop: sysY tem operatively connected to said pitch varying means comprising mechanism forlimiting pitch in the positive and negative pitch ranges, and means for selecting at least a portion of said mechanism for limiting in each of said ranges. Y

10. In a propeller according to claim 9 including mechanism for simultaneously operating said means for selectively connectingand means for selecting.

ll.` In a propeller-having variable pitch blades, means for varying the/pitch of said blades including a servo motorra source of-fluid under pressure, means for controlling ow ,of said fluid to said servo motor including a governor, 4manually operated Vmeans Vfor adjusting the speed setting'of said governor including a servo system, a

second 'manually operated means for overriding saidV governor -to vary the pressure in said servoy motor to feather the propeller blades, torque responsive means for overriding both said manual means to vary the pressure in said servo motor, and a valve operatively connected to said servo motor for overriding said manual means and said torque responsive means. n

12. In a propeller having variable pitch blades, means for varying the pitch'of said bladesin'positive ornegative ranges including a servo device, means` for controlling said servo device comprising a speed governor,Y

and a control valve regulated by said governor, means for setting the speed Yof said governor includingoperative connections thereto, and manually operable means for providing variable pitch stops throughout both said ranges and during feathering and` unfeathering of said blades including operative connections to said'valve, saidY connections including cam means andcamfollower means,

said cam follower means being kengageable with said 13; In acontrolif'r p y p blades, means for varying the pitch of said blades comprising a'servo device, Ameans for. controlling `said pitch varying means including a first control valve operatively connected to Vsaid servo device, a speed setting servo, manualmeans for adjusting said speed setting servo including a second control valve, a speed governor means for effecting -movement of said irst control valve, means forsetting'the speed of said governor meansincluding said speedsetting servo, a pitch stop mechanism open atively connected to said` control valve for urging said valve in opposition to said governor means in one direction, and means responsive to a functionv of movement of said servo device for varying the position of said stop A ated by said governor, sets of control lands on said control valve for positive and negative pitch control, means for selectively connecting one of said sets for controlling while disconnecting the other of said sets including snap action mechanism to avoid any dwell action including a hydraulic portion, and means connecting said snap action hydraulic` portion with said 'control valve.

Y Y References Cited in the leof this patent UNITD'STATES PATENTS Kopp r f July 1, 1947 42,612,958 Richardson v voct. 7, 1952 `2,613,750 Breguet a- Oct. 14, 1952 `2,640,555 Cushman June 2, 1953 2,664,959 1 Stuart Jan. 5, 1954 ,2,678,103 Martin et al May ll, 1954 2,737,253

` Moore et al. Mar. 6, 1956 fpropellerf having lvariable pitch 

